A gate-controlled HgCdTe long-wavelength infrared photoconductive detector

Abstract

A gated photoconductor structure is proposed for the dual purpose of enhancing the performance of and investigating surface effects in HgCdTe photoconductive infrared detectors. It is verified both theoretically and experimentally that the passivating native oxide which accumulates the HgCdTe surface, thereby quenching surface recombination, also causes excessive surface shunting and an overall reduction in device responsivity. It is found that for x = 0.23 Hg 1−x Cd x Te photoconductive detectors passivated with native oxide/ZnS the optimum surface conditions prevail at a gate bias corresponding to a semiconductor surface potential of 50 mV. Experimentally, it is found that operation at this optimum condition yields approximately a 70% increase in responsivity in comparison to floating gate conditions, which corresponds to a surface potential of 72 mV for the as-grown native oxide/HgCdTe interface. The gated photoconductor is shown to be a powerful diagnostic device structure that can be used to evaluate and optimize surface passivation layers for HgCdTe infrared detectors.

Noise modeling of shunt resistance in HgCdTe photoconductor detectors

“…This was investigated in detail in Refs. [15,16]. That is why we get peaked behavior in responsivity measurements of gated PC devices as was experimentally observed by Siliquini et al [15] and Pal et al [16].…”

“…Detailed results on dependence of lifetime on surface conditions such as Q ss , n ss and SRV are given in Ref. [14][15][16][17]. Hence for intermediate values of u s from 20 to 50 mV there is trade-off between increasing effective lifetime and increasing n 0s which effect shunt noise in opposite directions and hence a peak near 45 mV.…”

“…Additionally, Q ss is computed using results of standard one-dimensional model of MIS theory [13][14][15][16] …”

A Study of Sidewall Effects in HgCdTe Photoconductors Passivated with MBE-Grown CdTe

“…14 A trap ionization energy of 0.7E g , interface trap density of 8 9 10 12 cm À2 eV À1 on the unpassivated surface, and capture cross-section of 1 9 10 À17 cm À2 were used in the simulation. 15,16 CONCLUSIONS In this work, the effectiveness of CdTe as a passivating film for HgCdTe was studied. HgCdTe photoconductors with their surface fully passivated with CdTe show significantly higher photoresponsivity compared with devices without sidewall passivation, which indicates the effectiveness of the low-temperature MBE-deposited CdTe passivation layer in reducing surface recombination velocity.…”

Unified carrier density approximation for non-parabolic and highly degenerate HgCdTe semiconductors covering SWIR, MWIR and LWIR bands

“…This makes the surface highly n + with carrier density of the order of 10 17 -10 18 cm À3 . As a result, the normalized Fermi energy, /, at 77 K is very high at around 40-50 [3,4]. Hence, it is desirable to have an approximation of the Fermi integral for / > 10 for the case of passivated HgCdTe detectors.…”